Unable to nudge channels
I'm working on a project where I need to nudge and otherwise manipulate the individual channels in an RGB image. I've had the issue I'm about to describe happen before, but I've never a) been able to figure out what triggers it nor b) been able to resolve it once it happens.
Initially, after creating the image, I'm able to go to the Channels palette and use the move tool to move that channel. Or I can use the Transform tool to rotate or resize just that channel. At some point though, I am suddenly unable to manipulate the individual channels. I then get, for instance the following error:

The error message implies I can't move the 'data' because the target doesn't include all composite channels - but I don't want to move all the composite channels - I want to move just the, for instance, green channel. And just minutes before I was doing just that. I'm assuming here that 'the target' is the selected channel?
What am I missing? Thank you!
I've looked around and see that some people are able to resolve this by making sure they aren't editing in Quick Mask mode. I've checked that...
